SCIENCE IN THE NEWS DAILY
Electric Material in Mantle Could Explain Earth's Rotation
from ScienceNOW Daily News
When it comes to Earth's rotation, you might think geophysicists have pretty much everything
figured out. Not quite. In order to explain some variations in the way our planet spins, Earth's
mantle--the layer of hot, softened rock that lies between the crust and core--must conduct
electricity, an ability that the mantle as we know it shouldn't have. Now, a new study finds that
iron monoxide, which makes up 9% of the mantle, actually does conduct electricity just like a
metal, but only at temperatures and pressures found far beneath the surface.
Earth's spin isn't flawless. Geophysicists have discovered that the time it takes our planet
to complete one rotation--the length of a day--fluctuates slightly over the course of months or
years. They've also noticed extra swing in the predictable wobble of Earth's axis of rotation,
like the swaying of a spinning top. The variations are probably caused by the solid iron inner
core, liquid metal outer core, and rocky mantle rotating at slightly different rates.
Friction helps bring them into line, and the magnetic field of the outer core can pull on the
metal inner core. But to really fit the observations, the core should also exert its magnetic tug
on the mantle, says Bruce Buffett, an earth scientist at the University of California, Berkeley,
who was not involved in the new study. This means that a layer of the mantle must be able to
conduct electricity. But, he says, "the origin of the metallic layer remains an open
question."
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